1. Field of the Invention
The present invention relates to an absolute angle detecting device applicable to, for example, a steering angle sensor of a car, and more particularly, to a device that allows a control device to easily process signals.
2. Description of the Related Art
As the related art, there has been known a technique in which an absolute angle detecting device is provided between a steering shaft and a chassis of a car, and various control operations, such as the attenuation force control of a suspension, the shift position control of an automatic transmission, and the steering control of rear wheels of a car with four-wheel drive, are performed on the basis of, for example, the steering angle, steering speed, and steering direction of a steering wheel detected by the absolute angle detecting device.
The steering wheel (steering shaft) is constructed so as to make one or more rotations whenever it shifts from the neutral position to the right side and the left side. Therefore, an absolute angle detecting device formed by a combination of a rotation detecting unit for detecting a rotation angle within one revolution and a rotation detecting unit for detecting a rotation angle over one revolution is used to detect the steering angle of the steering shaft.
Further, as the related art, there have been suggested various absolute angle detecting devices in which an increment-type encoder for accurately detecting the rotation angle of a steering wheel within one revolution is composed of a code plate that integrally rotates with the steering wheel and a photo-interrupter that is arranged to face the code plate; an absolute-type encoder for roughly detecting the rotation angle of the steering wheel over one revolution includes a rotor member which integrally rotates with the code plate, a stator member which rotatably supports the rotor member, a rotary member which is concentrically arranged with the center of rotation of the rotor member, a relay gear which is rotatably supported by the rotary member, and a detecting element which detects the rotation amount of the rotary member; the relay gear intermittently engages with engaging projections provided on a circumferential surface of the rotor member; and the relay gear always engages with a driven gear provided in the stator member (for example, see Japanese Unexamined Patent Application Publication No. 10-227631 (FIGS. 5 to 8)).
The detecting element is used of an optical type using, for example, a photo-interrupter or a photo-reflector, a magnetic type using, for example, a magnet and an MR element or a hole element, or a contact type using, for example, a brush and a resistance pattern.
A control device mounted on a vehicle acquires signals respectively output from the rotation detecting unit for detecting the rotation amount of the steering wheel within one revolution and the rotation detecting unit for detecting the rotation amount of the steering wheel over one revolution to calculate the absolute angle of the steering wheel, and then generates various control signals on the basis of the calculated absolute angle.
As described above, the control device mounted on the vehicle acquires signals output from the respective rotation detecting units to calculate the absolute angle of the steering wheel. However, as in the absolute angle detecting device disclosed in Japanese Unexamined Patent Application Publication No. 10-227631, when the absolute angle within one revolution is signal-processed on the basis of code signals output from the increment-type encoder, and when the rotation amount over one revolution is signal-processed on the basis of signals output from the absolute-type encoder, which is different from the code signals, an algorithm for signal processing is complicated, which makes it difficult to process signals at high speed. In addition, in this case, a lot of signal processing circuits are needed, which makes it difficult to manufacture an absolute angle detecting device with low costs.